Topiramate is a new anticonvulsant drug recommended for treatment of partial and generalized seizures in children and adults. It has been found to cause a nonanion gap metabolic acidosis in some patients, which is related to carbonic anhydrase inhibition. This adverse reaction is more common in children than adults and is rarely symptomatic. Clinicians need to be aware of this potential side effect especially in children undergoing major surgery. Children who are treated with topiramate should have a careful history taken preoperatively looking for signs of a metabolic acidosis and baseline blood chemistries should be measured prior to surgery to detect an asymptomatic metabolic acidosis.